Largely enhanced ferromagnetism in CuO nanoparticles by tungsten doping

Cu1-xWxO (x = 0.0, 0.01, 0.02, and 0.04) nanostructures (synthesized via the co-precipitation method) were characterized by different techniques and their magnetic properties were analyzed. Rietveld refinement method proved that the tungsten substitution preserves the CuO crystalline phase, with a slight modification in the lattice parameters. x = 0.02 sample refinement exhibited a minor peak associated with the WO3 secondary phase which was not necessary to include in the refinement; for higher doping levels it was necessary to include this secondary phase in the refinement. IR bands changes were attributed to lattice variations and crystal defects. SAED patterns allowed to calculate interplanar distances associated to the CuO crystallographic planes, in most of the cases. XPS confirmed that W6+ is the precise form of W ions in the W-doped CuO. Magnetic response increased of the CuO to x = 0.01 sample for temperatures between 50 and 200 K. x = 0.02 sample exhibited a remarkable ferromagnetic behavior which was attributed to the complete inclusion of dopant; that material also exhibited the higher remnant magnetization. The ferromagnetic response decreased by increasing tungsten concentration until 4%. Hence, the remarkable magnetic characteristics of the x = 0.02 material were not explained by the presence of WO3 secondary phase, due to this appears in greater proportion in the x = 0.04 sample, and in this material the ferromagnetic behavior was significantly inhibited. Overall, the tungsten doping influence on the CuO magnetic properties may be explained by the creation of defects and lattice distortions.